The contractor shall produce uniformly labeled (100% incorporation) carbohydrates: xylose, galactose, and mannose. These compounds will be used in non-invasive diagnostic techniques (i.e. breath testing, magnetic resonance imaging), and in the research community for metabolic studies that may ultimately lead to the development of new non-invasive diagnostic tools. The labeled compounds will be produces by autotrophic growth of high polysaccharide producing strains of microalgae, using 13C as the sole carbon source.